Last summer I heard about potato boxes and decided to try using one this year.
When growing potatoes in the traditional way, you plant a seed potato and as the plant grows you keep hilling dirt up around its base, because new potatoes all grow above the seed and below the top of the dirt; hilling maximizes the vertical space available for the potatoes to grow in.
The idea of a potato box is to increase the vertical space even more, by planting in a box and then raising the level of the dirt and the box's sides simultaneously. There are a number of plans for such boxes online; there's a good example here.
I decided that I wanted to build something that could be easily disassembled. Some people pile up old car tires and fill them with dirt, which is certainly minimal in effort required, if not aesthetically delightful. A friend is putting together 4x4 squares that can be piled on top of each other; fairly straightforward, apart from the mortise and tenon joints that he's using to assemble them. But these options don't allow access to the lower levels of the box, and one of the things I liked about the plans noted above is that you can get at the potatoes from the bottom and work your way up as the plant grows. We don't have oodles of cool, dry space to store oodles of potatoes, so being able to pick on an ongoing basis seemed like a great idea.
So ease of assembly/disassembly and the ability to access from the bottom without disturbing the upper growth is important. I spent some time sketching possible plans and finally came up with something that I thought would do everything I want it to. The plans underwent some modifications as I worked on building the thing, and there's one part that I think may still need some modifications, but I think the basic design is sound. (It would never have gotten it done at all without Pericat's advice, Pericat's problem-solving skills, and Pericat's tools, as Peri is the carpentry brains around here, but that's another story.) In any case, it's up and planted with potatoes!
Here's what the basic structure looks like:
There are two solid sides (we'll say east and west) that are joined by connectors in a reasonably stable structure; at each end the verticals are paired. The north and south sides are built from loose boards that can slide between the paired 2x2s of the east/west sides.
Here's how it was constructed.
Start by putting together the two east/west sidepieces from 2x2s. I used 28" long pieces for the horizontals and 36" pieces for the verticals.
Before you start to actually assemble them, you MUST get your supplies together and do some measuring. (Note for the inexperienced: as anyone who works with wood knows, the real dimensions of wood are NOT the same as the dimensions given in the names at a lumberyard—a 2x2, for example, is actually approximately 1.5 x 1.5—so DON'T make calculations based on what the wood you are buying is called.)
Each side has TWO verticals at each end. The boards for the north and south sides slide between these verticals, supported by small L brackets, so it's important to make sure that you leave enough room for the combination of brackets and boards but not too much.
Mark positions for the two verticals against the horizontal 2x2. Make sure you leave enough space between them to allow for the brackets (and screwheads, if they aren't flush) and free movement of the sliding boards. I used L brackets that had a real dimension of about 3/4", so I left exactly 1 inch between the verticals, and that worked very well.
I measured up from the bottom horizontal in order to figure out where the first bracket should go, and then up again for the next bracket, and so on. I left just enough space for the boards to slide easily but not so much that dirt could easily leak out between them. Your measurements for bracket position will vary depending on the size of boards you use. I used 1 x 8 boards (which is really only 7 3/8, not 8") and allowed 7.5", measured between bracket screwholes.
Before committing completely to all brackets and the spacing between verticals, do a test with a small section of board to ensure that your calculations will work with your materials!
Once the measuring was done, I drilled holes, attached the brackets, and screwed the 2x2s together with 1.5" woodscrews (the kind used for outdoor decking).
Next screw one or two boards to the frame to make the base of a solid side and give the structures some stability. These boards should rest on the bottom horizontal 2x2 of the frame and only go to the width of the inner verticals of each pair, as shown in this drawing.
When you build above the boards that are screwed into place, you should be able to do it by resting the boards on top of each other and relying on the weight of the dirt to hold them in place.
Once you've got the east and west sides built, connect them using a single 2x2 bar at the top; it's attached to each side by a 4" bolt run through drilled holes (3.5" would have worked but the lumberyard was out of them). These would probably hold even without nuts, but I used nuts so the parts wouldn’t fall apart while I was getting things in place.
In the original design I intended to repeat the top connecting bar on the bottom to finish it off, but it quickly became clear that doing so would cause problems: either it would interfere with the side boards or it would have to go under the whole thing and thus prevent the box from sitting flat unless a trench was dug.
So instead I ran additional connectors on both sides of the bottom. They tuck quite neatly above the horizontal 2x2s on the bottom of the east/west sides, just outside where the loose boards fit. (Ignore the weathered board in the background of this photo, it's not part of the potato box.)
I've drilled holes through them for bolts to drop through. Because the 2x2 underneath has a screw through it from holding the vertical 2x2s in place, I can't drill a hole right through it, but I could drill in about half an inch. The bolt therefore can't be held in place by a nut, but the center bar holds the 2 sides securely at the bottom and the side stabilizers therefore just have to keep the angles of the box sides from skewing. This is what the drawing and photo show. It's not a great solution, but it seems to work.
If I did it again, I would shove the two stabilizing 2x2s right up against the sideboards—I think this would provide room for the drill hole to go through the space between the screws holding the vertical 2x2s in place. The loose sideboards would then rest on top of the stabilizing 2x2s. But because of the limited space into which I was putting the box, I had already put the bottom loose sideboards in place, so they were in the way and I didn't think of that. Never mind, I'll modify it when I put it together again next year. At that point it should look like this:
Now the box is ready (and, presumably, in place). All that's left is to slide in the first loose boards on north and south and then build them up with the rest of the box as the project proceeds. And here's what it looks like in real life! I will post the results of this grand experiment when they are harvested.
